Cubic magnetic anisotropy of nonstoichiometric magnetite

The cubic magnetic anisotropy constants of Fe_3(1-δ){O}₄$ single crystals (with 0.0000.006), obtained by curve fitting of the respective magnetization curves, are reported between room temperature and the isotropic point ({~}130 K), where the easy axis changes from [111] to [100]. Two distinct temperature dependences are observed for nonstoichiometries above and below δC=0.0039, in samples with second- and first-order Verwey transitions, respectively. The characteristic temperatures for the first-derivative curves are consistent with mean-field parameters for nearest-neighbor-interaction models.